This invention relates to a new system for fixing the stator nozzles to a power turbine casing in a simple, rational, rapid and effective manner.
In order to keep a power turbine stator casing as cold as possible, the stator blades or nozzles traversed by the hot gas are not fixed directly to the stator casing, but instead are combined into sectors, each of two or three nozzles, and are insulated from the stator casing by means of spacer-supports of material which is a poor conductor of heat, known as shrouds.
In the present state of the art, the system most widely used for connecting the nozzle sectors to the shrouds and for connecting these latter to the stator casing uses connection pins or bolts, which make it necessary to form either through or threaded holes in the members to be connected together, according to requirements. However, such a method gives rise to considerable drawbacks due in particular to the fact that said holes constitute a dangerous triggering point for cracks which originate as a result of machine "thermal fatigue" phenomena, and can lead to the fracture of various components, thus considerably limiting the thermal fatigue life of said components.
Another frequent and very annoying drawback is due to the accidental fall of the fixing nut while being screwed on to the threaded shank, leading to a considerable loss of time by virtue of the fact that the nut has to be sought in the rotor.
Again, the known method does not allow those components bolted together to undergo differential thermal expansion in a radial direction, as would be desirable, and in addition allows the "throat area" tolerances between one nozzle sector and the two adjacent sectors to be respected only by using complicated systems involving the use of a nozzle carrier ring, an adjustment operation on the nozzle at the moment of mounting the ring, and the use of two eccentric pins in order to fix the nozzles in the position in which they lie after being mounted in the nozzle carrier ring.